Cardiac mitochondria sustain damage during
ischemia and reperfusion, contributing to cell death. The reversible blockade of electron transport during
ischemia with
amobarbital, an inhibitor at the
rotenone site of complex I, protects mitochondria against ischemic damage.
Amobarbital treatment immediately before
ischemia was used to test the hypothesis that damage to mitochondrial respiration occurs mainly during
ischemia and that protection of mitochondria during
ischemia leads to decreased cardiac injury with reperfusion. Langendorff-perfused Fischer-344 rat hearts were treated with
amobarbital (2.5 mM) or vehicle for 1 min immediately before 25 min of global
ischemia. Both groups were reperfused for 30 min without additional treatment. Subsarcolemmal (SSM) and interfibrillar (IFM) populations of mitochondria were isolated after reperfusion.
Ischemia and reperfusion decreased state 3 and increased state 4 respiration rate in both SSM and IFM.
Amobarbital treatment protected oxidative phosphorylation measured following reperfusion and improved the coupling of respiration.
Cytochrome c content measured in SSM and IFM following reperfusion decreased in untreated, but not in
amobarbital-treated, hearts. H(2)O(2) release from SSM and IFM isolated from
amobarbital-treated hearts during reperfusion was markedly decreased.
Amobarbital treatment before
ischemia improved recovery of contractile function (percentage of preischemic developed pressure: untreated 51 +/- 4%, n = 12;
amobarbital 70 +/- 4%, n = 11, p < 0.01) and substantially reduced
infarct size (untreated 32 +/- 2%, n = 7;
amobarbital 13 +/- 2%, n = 7, p < 0.01). Thus, mitochondrial damage occurs mainly during
ischemia rather than during reperfusion. Reperfusion in the setting of preserved mitochondrial respiratory function attenuates the mitochondrial release of
reactive oxygen species, enhances contractile recovery, and decreases
myocardial infarct size.